1. Field of the Invention
The present invention relates to color image processing apparatus such as, for example, digital color copying devices or digital color facsimile devices.
2. Related Background Art
In conventional color image processing apparatus of this type, a color original document is input as three different color signals, so that three different color (red, green and blue) filters are sequentially selected to separate corresponding colors, the corresponding images are scaled down by optical systems and collected on photo receptors such as a one-dimensional CCD to read the color signals.
Recently, a one-dimensional contact-type color sensor is often used in order to increase the quantity of light impinging on a CCD to enhance the S/N ratio, reduce the external dimensions of the color-document reader and facilitate the adjustment of optical systems such as lenses.
As shown in FIG. 2A, the contact-type color sensor includes a total of five CCD chips 200-204, about 50 mm long, arranged in staggered relationship so as to be able to read the 297 mm lateral range of an A-4 sized page. The filters for color separation are formed by putting down three layers of red, green and blue coloring matter on the CCD, as shown in FIG. 2B.
There is the problem that if a sheet of a document is read by those five CCD sensors 200-204, the balance among three colors for the five channels will be lost due to variations in the characteristics of the color separation filters among the five channels, the spectral sensitivity of the photo receptors, etc., thus, colors will vary from channel to channel.